The invention relates to printed circuit boards, and more particularly to a printed circuit board that creates electrical connections with electrically conductive ink.
Single-sided circuit boards with conductive jumpers or cross-overs are often used to increase the number of connections on the printed circuit board without resorting to more expensive double-side circuit boards. In a circuit having two conductive pads, or xe2x80x9cviasxe2x80x9d that are separated by conductive traces, the vias are connected together by first applying an electrically insulating undercoat layer on the traces, then applying electrically conductive ink onto the insulating layer to form a path connecting the vias. To protect the path, an insulating overcoat layer is applied on top of the conductive ink.
Although this structure does connect the vias, moisture and/or a positive electrical field across the conductive ink may cause the conductive ink to migrate, degrading the quality of the path and causing the conductive ink to even migrate through the undercoat and overcoat, creating undesirable short circuits. More particularly, any water in the undercoat or overcoat layer will polarize when exposed to an electrical field. If the electrical field is positive with respect to the undercoat or overcoat, particles from the conductive ink will travel through the undercoat/overcoat material, creating short circuits between the cross-over and nearby electrical contacts on the circuit board.
There is a desire for a circuit board structure that incorporates conductive ink cross-overs without experiencing migration problems.
The present invention is directed to a circuit board having cross-over structures incorporating two types of conductive ink: a conventional, conductive ink and an enhanced ink having enhanced properties to minimize or prevent migration of the conductive ink.
In one embodiment, the enhanced ink is applied directly on top of the conductive ink on an undercoat layer before applying the overcoat. The direct contact between the conductive ink and the enhanced ink causes the two inks to be at the same voltage potential, eliminating formation of a positive electrical field between the overcoat and the cross-over.
In another embodiment, the overcoat is sandwiched between the conductive ink and the enhanced ink, creating an improved moisture barrier on the overcoat. The enhanced ink may be formed into multiple traces, connecting the traces into one or more groups, and then tying each group to the highest voltage potential in the vicinity of the group. This ensures that the electric field between the conductive ink and the enhanced ink is either zero or negative, preventing migration of the conductive ink.
In yet another embodiment, the insulating material normally used to form the overcoat layer is eliminated and two layers of the enhanced ink are applied to the conductive ink as the overcoat. Because the lower layer of the enhanced ink contacts both the conductive ink and the upper enhanced ink layer, all three layers are at the same voltage potential, eliminating electrical fields in any of the layers.
By using the enhanced ink to eliminate moisture and/or positive electric fields around the conductive ink path, the invention prevents short circuits from occurring due to migration of the conductive ink through the undercoat and/or overcoat layers.